Phosphating solutions



United States Patent 3,116,178 PHOSPl-IATENG SOLUTIONS Wesley B. Upharn, Melrose Park, Fort Lauderdale, Fla, assignor to The lliuhrizol orporation, Wicltlifie, Ohio, a corporation of Ohio No Drawing. Filed May 29, 1961, Scr. No. 113392 '7 (Ilaims. (Cl. 1486.15)

This invention relates to improved aqueous phosphating solutions. In a more particular sense it relates to aqueous phosphating solutions having reduced tendency to form blush rust on ferrous metal surfaces.

it is known in the metal finishing art to provide metal surfaces, especially ferrous surfaces, with an inorganic phosphate coating by contacting them with an aqueous phosphating solution. The phosphate coating protect the metal surface against corrosion and serves as an excellent base for the later application of organic coatings such as paint, lacquer, varnish, enamel, and the like.

Such inorganic phosphate coatings are generally formed on a metal surface by means of aqueous solutions which contain the phosphate ion and, optionally, certain auxiliary ions including 'metallic ions such as manganese, zinc, iron, copper, lead, nickel, cobalt, and antimony ions, and non-metllic ions such as ammonium, chloride, bromide, nitrate, and chlorate ions. These auxiliary ions modify the character of the phosphate coating and adapt it for a wide variety of applications.

The preparation and use of aqueous phosphating solutions is well-known in the metal finishing art as shown by U.S. Patents 1,206,075; 1,247,668; 1,305,331; 1,485,025; 1,610,362; 1,980,518; 2,001,754; and 2,859,145.

Aqueous phosphating solutions are generally prepared by dissolving in water minor amounts of phosphoric acid and, optionally, a metal salt such as a nitrate, phosphate, nitrite, sulfate, chloride, or bromide of manganese, zinc, iron, nickel, copper, lead, or antimony. Ordinarily an oxidizing agent such as sodium chlorate, potassium per borate, sodium nitrate, ammonium nitrate, sodium chlorite, potassium perchlorate, or hydrogen peroxide is included in the phosphating solution to depolarize the metal surface being treated and thereby increase the rate at which the phosphate coating is formed on the metal surface. Other auxiliary agents such as anti-sludging agents, coloring agents, and metal cleansing agents may also be incorporated in the phosphating solution. One common type of commercial phosphating bath which contains the zinc ion, the phosphate ion, and a depolarizer is made by dissolving small amounts of zinc dihydrogen phosphate, sodium nitrate, and phosphoric acid in water.

in order to provide the commercially satisfactory coating weights and coating speeds, an aqueous phosphating solution should have a total acidity within the range from about 5 to about 100 points, and preferably from about 5 to about 50 points. The term points acidity as employed in the phosphating art represents the number of milliliters of 0.1 normal sodium hydroxide solution required to neutralize a milliliter sample of a phosphating solution in the presence of phenolphthalein as an indicator.

A particularly desirable and effective class of aqueous phosphating solutions or baths is set forth in the co-pending application of John A. Henricks, Serial No. 373,449, filed August 10, 1953, and owned by the assignee of the present invention. It is intended that the disclosure of the said Henricks application be considered as forming a part of the present specification. The phosphating solutions described therein have a toal acidity within the range from about 5 to about 100 points and contain as essential ingredients of zinc ion; the phosphate ion; nitrate ion; and an ion selected from the group consisting of til ans

2, lithium, beryllium, magnesium, calcium, strontium, cadmium, and barium ions. Such phosphating solutions provide a dense, adherent, micro-crystalline or amorphous phosphate coating which shows substantially no visible crystal structure at a magnification of diameters and which is preferred for the purpose of the present invention.

In View of the extensive commercial development of the phosphating art and the many journal publications and patents ldescribing the application of phosphating solutions, it is believed unnecessary to lengthen this specification unduly by a detailed recitation of the many ways in which the phosphating step may be accomplished. Suffice it to say that any of the commonly used phosphating techniques such as spraying, brushing, dipping, or rollercoating may be employed, and that the temperature of the aqueous phosphating solution may vary within wide limits, e.g., from room temperature to about 212 F. In general, best results are obtained when the aqueous phosphating solution is used at a temperature within the range of from about F. to about 210 F. If desired, however, the aqueous phosphating bath may be used at higher temperatures, e.g., 225 F., 250 F., or even 300 F, by employing superatmospheric pressures.

in the ordinary practice of phosphating a metal surface, such surface is first cleaned by physical and/ or chemical means to remove any grease, dirt, or oxides and then it is phosphated in the manned described above.

The phosphating operation is usually carried out until the weight of the phosphate coating formed on the metallic surface is at least about 25 milligrams per square foot of surface area and is preferably Within the range from about 100 to about 1000 milligrams per square foot of surface area. The time required to form the phosphate coating will vary according to the temperature, the type of phosphating solution employed, the particular technique of applying the phosphating solution, and the coating weight desired. In most instances, however, the time required to produce a phosphate coating of the weight preferred for the purpose of the present invention will be Within the range of from about one-quarter minute to about 15 to 20 minutes.

Upon completion of the phosphating operation, the phosphated article is rinsed, optionally, with water and/ or a dilute aqueous solution of chromic acid containing from about 0.01 to about 1.0 percent of CrO The chromic acid rinse appears to seal the phosphate coating and improve its utility as a base for the application of paint, lacquer, Varnish, and the like.

One problem common to all of these known phosphating solutions and phosphating techniques is their tendency to form a thin film of iron oxide or blush rust on a ferrous metal surface. The blush rust phenomenon is particularly prevalent in spray-phosphating operations where the ferrous article is surrounded by a hot, humid atmosphere containing oxygen, water vapor, and fine droplets of the phosphating solution. Under these conditions, two competing reactions occur, viz., an oxidation of the ferrous surface by the water vapor-oxygen mixture and the desired reaction of the phosphating solution with the ferrous surface. The former reaction is believed to be responsible for the formation of blush rust.

Attempts have been made to suppress the formation of blush rust by the addition of passivating agents such as metallic nitrites and metallic dichromates to the phosphating solution. Although these efforts have been more or less successful in reducing the incidence of blush rust, they have introduced certain new problems, principally a greater rate of sludge formation in the phosphating bath in the case of nitrites, and a reduction in coating weights and coating speeds in the case of dichromates. Under certain operating conditions, metal dichromates passivate the ferrous surface to such an extent that it will no longer receive a phosphate coating.

It is an object of the present invention to provide improved aqueous phosphating solutions.

It is a further object to provide phosphating solutions which reduce the incidence of blush rust.

Another object is to provide a convenient and economieal process for phosphating ferrous metal surfaces which reduces the formation of blush rust Without adversely affecting the sludging or coating characteristics of the phosphating solution.

These and other objects are achieved by incorporating in an aqueous phosphating solution the anions of a polyhydroxy aliphatic monocarboxylic acid.

In its broadest aspect, the present invention is directed to an aqueous phosphating solution having a total acidity within the range from about 5 to about 100 points and containing as essential ingredients the phosphate ion and the anion of a polyhydroxy aliphatic monocarboxylic acid.

In a more particular sense, the present invention is directed to an aqueous phosphating solution having a total acidity within the range from about 5 to about 100 points containing as essential ingredients the Zinc ion, the phosphate ion, and the anion of a polyhydroxy aliphatic rnonoearboxylic acid.

In its preferred embodiment, the present invention is directed to an aqueous phosphating solution having a total acidity within the range from about 5 to about 100 points and containing as essential ingredients the zinc ion, preferably in an amount from about 0.1 to about 1.0 percent; the phosphate ion, preferably in an amount from about 0.25 to about 2.0 percent; the nitrate ion, preferably in an amount from about 0.25 to about 8.0 percent; an ion selected from the group consisting of lithium, beryllium, magnesium, calcium, strontium, cadmium, and barium ions, preferably in an amount from about 0.1 to about 4.0 percent; and at least about 0.1 percent of the anion of a polyhydroxy aliphatic monocarboxylic acid.

Best results, both from the standpoint of the excellence of the phosphate coating and the suppression of the blush rust, are obtained with an aqueous phosphating solution having a total acidity within the range from about 5 to about 50 points and containing as essential ingredients from about 0.1 to about 0.6 percent of Zinc ion; from about 0.3 to about 1.5 percent of phosphate ion; from about 0.5 to about 6.0 percent of nitrate ion; from about solutions of this invention may be supplied conveniently by the free acid or a salt thereof. Thus, for example, an addition to the phosphating solution of the free polyhydroxy aliphatic monocarboxylic acid, its ammonium salt, or its light or heavy metal salt, such as, e.g., a sodium, potassium, lithium, calcium, strontium, barium, copper, lead, or nickel salt, serve equally well for the purpose of the invention. It appears to be of no consequence whether the acid or salt is used, just as long as the cation of the salt is one which has no adverse effect upon the coating characteristics of the solution. Likewise it appears to be of no consequence whether a mixture of clirlerent acids, diiferent salts, or different acids and salts is used.

Polyhydroxy aliphatic monocarboxylic acid compounds which are well suite-cl for the present invention include principally those acids which contain at least 5 carbon atoms and at least 3 hydroxy groups in the molecule. Such acids are readily available from the controlled oxidation of aldose sugars and include, for example, acids such as gluconic acid, hexahydroxyheptanoic acid, mannoheptonic acid, mannonic acid, idonic acid, galactonic acid, rhamnohexonic acid, rhamnoic acid, rhamnoheptonic acid, rhamnooctonic acid, rhamnotetronic acid, glucoheptonic acid, mannooctonic acid, gluco-octonic acid, galaheptonic acid, gala-octonic acid, glucononoic acid, mannononic acid, and octahydroxy-arachidic acid.

By reason of their commercial availability, stability in storage, and low cost, the alkali metal salts and especially the sodium salts are preferred as a source of the anion of the polyhydroxy aliphatic monocarboxylic acid. A par ticular preference is expressed for sodium gluconate and sodium hexahydroxyheptanoate.

The polyhydroxy aliphatic monocarboxylic acid compound is generally employed in an amount sufficient to impart at least about 0.1 percent by weight and preferably from about 0.2 to about 5.0 percent of the acid anion to the phosphating solution. Amounts of anion below about 0.1 percent appear to have little effect in reducing blush rust and amounts over 5.0 percent, although effective, contribute little added protection and are uneconomical. From the standpoint of both economy and eifectiveness, amounts between about 0.25 and about 1.5 percent are particularly preferred.

Specific examples of phosphating solutions of the present invention are shown in Table I (except for the Points total acid, the values given indicate the percentages by weight of the several ions in the phosphating solution):

TABLE I Ion Phosphating Solution Cu Polyhydroxy aliphatic carboxylie acid anion Points total acid 1 G'lueonie acid anion.

2 llexahydroxyhcptanoic acid anion. 3 Rhamnehexonic acid anion.

4 Rhamnonic acid anion.

5 Glyeo-octonic acid anion.

6 Gala-octonie acid union.

1 Gluconononic acid anion.

0.1 to about 1.5 percent of calcium ion; and from about 0.2 to about 5.0 percent of the anion of a polyhydroxy aliphatic monocarboxylic acid having at least 5 carbon atoms and at least 3 hydroxy groups.

The anions of the polyhydroxy aliphatic monocarbox- The preparation of certain of the above phosphating solutions is carried out as follows:

Solution A 4.98 g. of Zn(NO 6.88 g. of NaH PO 6.32 g. of

Ca(NO -3H O and 2.5 g. of sodium gluconate are ylic acid used to suppress blush rust in the phosphating dissolved in sufficient water to make: one liter of solution.

tion A, except that 2.5 g. of sodium hexahydroxyheptanoate is used in lieu of the sodium gluconate.

Solution C A mixture of 1.95 ml. of 42 Baum HNO and 4.66 ml. of commercial 75% 111 1 is neutralized with 1.92 g. of ZnO and 1.46 ml. of 50% aqueous NaOH. Then 20 g. of Ca(NO -3H O and g. of sodium hexahydroxyheptanoate are added and the whole is diluted with sufiicient water to make one liter of solution.

Solution D 14.2 g. of Zn(NO '6H O, 7.8 g. of commercial 75% H POA 4.2 g. of ZnCl 8.7 g. of NH H PO 14.3 g. of Ca(NG -3H O, and 1.0 g. of rhamnohexonic acid are dissolved in suificient water to make one liter of solution.

Solution E 21.4 g. of Z11(NO '6H O, 7.2 g. of commercial 75% HgPO g. Of NH4H2PO4, g. Of Ca(NO -3H O, and 10 g. of rhamnonic acid are dissolved in sufiicient water to make one liter of solution.

Solution M A concentrate is first made by dissolving 1.75 lbs. of manganous dihydrogen phosphate, 5.0 lbs. of 84% H PO 0.5 lb. of NaNO and 0.016 lb. of cupric nitrate in enough Water to yield one gallon of concentrate. This concentrate is then diluted with 32 gallons of water and 4.8 lbs. or" hexahydroxyheptanoic acid is dissolved in the solution.

Solution N 2.35 lbs. of manganous carbonate is allowed to react with a mixture of 0.5 gallon each of water and 75% commercial 11 E 0 After the evolution of CO has subsided, 6.3 lbs. of gala-octonic acid is added and the Whole is diluted with suficient Water to yield 50 gallons of solution.

The following examples are submitted to set forth speciiic modes of applying the invention. They are intended for purposes of illustration only and are not to be construed as limiting the scope of the invention.

EXAMPLE 1 Solution A and 3 similar phosphating solutions containing larger or smaller quantities of sodium gluconate than Solution A were prepared. A control solution similar to Solution A but not containing sodium gluconate was also prepared.

Each solution was heated to 200 F. and used to phosphate a 3-inch square test panel of clean, solventdegreased, gauge cold-rolled steel. A test panel was immersed in each solution for 10 seconds, suspended in the vapor above the hot solution for one minute and then removed to a rack and allowed to dry.

An inspection of the test panels for blush rust yielded the following data:

EXAMPLE 2 A series of experiments like those carried out in example 1 were conducted using phosphating Solution B, two solutions similar to Solution B but containing larger quantities of sodium hexahydroxyheptanoate, and a control solution similar to Solution B but not containing sodium hexahydroxyheptanoate. were as follows:

The results obtained Percent hexahydroxy-hcptanoic acid anion in the Blush rust phosphating solution formation EXAMPLE 3 Solution C, 4 similar phosphating solutions containing smaller quantities or" sodium hexahydroxyheptanoate, and a control solution similar to Solution C but not containing sodium hexahydroxyheptanoate were employed for the spray-phosphating of 4 x 8-inch 20 gauge cold-rolled steel test panels.

The overall phosphating operation was carried out as follows: Each of six solvent-degreased, 4 x 8-inch test panels was bent 180 degrees along its 4-ineh dimension on a conical mandrel. Each of the formed panels was sprayed for 1 minute at 170180 F. with an aqueous solution containing 2 ounces/ gal. of a commercial alkaline cleanser, sprayed for 3 minutes at F. with tap Water, and then sprayed with the selected phosphating solution for 2 minutes at 165 F. While each formed panel was still Wet with phosphating solution, it was spray-rinsed successively with cold tap Water for 1 minute and warm (90 F), dilute aqueous chromic acid (0.125 g. CrO /liter) for 1 minute.

After the panels had dried, they were inspected for blush rust formation on the convex and the concave surfaces:

None (control) 0. 3

(Solution 0) EXAMPLE i A full-scale evaluation of the effectiveness of a phosphating solution of this invention was conducted in a plant where steel bodies for pickup trucks were sprayphosphated prior to painting. The use of a phosphating solution similar to Solution C but not containing sodium hexahydroxyheptanoate had resulted in the formation of blush rust on certain portions of the bodies, principally the tail-light, front-panel, under-fender, under-cab, and spare tire well areas.

The use of a phosphating solution similar to Solution C but containing 0.3 percent sodium hexahydroxyheptanoate substantially reduced the incidence of blush rust. Visual inspections of a large number of cabs which had been phosphated with this solution yielded the following data (made with reference to results obtained wth the phosphating solution which did not contain sodium hexahydroxyheptanoate) Area inspected Inspectors remarks Tail-light Front-panel Undcrendcr Under-cab. l. Spare the well 90% elimination of blush rust.

7 and containing as essential ingredients the phosphate ion and the anion of a polyhydroxy aliphatic monocarboxylic acid having at least carbon atoms and at least 3 hydroxy groups.

2. An aqueous phosphating solution having a total acidity within the range from about 5 to about 100 points and containing as essential ingredients the zinc ion, the phosphate ion, and the anion of a polyhydroxy aliphatic monocarboxyl-ic acid having at least 5 carbon atoms and at least 3 hydroxy groups.

3. An aqueous phosphating solution having a total acidity Within the range from about 5 to about 100 points and containing as essential ingredients the Zinc ion; the phosphate ion; the nitrate ion; an ion selected from the group consisting of lithium, beryllium, magnesium, calcium, strontium, cadmium, and barium ions; and the anion of a polyhyd-roxy aliphatic monocarboxylic acid having at least 5 carbon atoms and at least 3 hydroxy groups.

4. An aqueous phosphating solution having a total acidity within the range from about 5 to about 100 points and containing as essential ingredients from about 0.1 to about 1.0 percent of Zinc ion; from about 0.25 to about 2.0 percent of phosphate ion; from about 0.25 to about 8.0 percent of the nitrate ion; from about 0.1 to about 4.0 percent of an ion selected from the group consisting of lithium, beryllium, magnesium, calcium, strontium, cadmium and barium ions; and at least about 0.1 percent of the anion of a polyhydroxy aliphatic monocarboxyl-ic acid 8. An aqueous phosphating solution having a total lacidlty within the range from about 5 to about 50 points i and containing as essential ingredients from about 0.1 to

having at least 5 carbon atoms and at least 3 hydroxy groups.

about 0.6 percent of zinc ion; from about 0.3 to about 1.5 percent of phosphate ion; from about 0.5 to about 6.0 percent of nitrate ion; from about 0.1 to about 1.5 percent of calcium ion; and from about 0.2 to about 5.0 percent of the anion of a polyhydroxy aliphatic monocarboxylic acid having at least 5 carbon atoms and at least 3 hydroxy groups.

6. An aqueous phosphating solution in accordance with claim 5 wherein the anion of the poly'nydroxy aliphatic monocarboxylic acid is the anion of gluconic acid.

7. An aqueous phosphating solution in accordance with claim 5 wherein the anion of the polyhydroxy aliphatic monocarboxylic acid is the anion of hexahydroxyheptanoic acid.

References Cited in the file of this patent UNITED STATES PATENTS 1,911,537 Tanner May 30, 1933 2,481,372 Fuchs et al. Sept. 6, 1949 2,499,261 Rosenbloom Feb. 28, 1950 2,529,178 Nieland et a1. Nov. 7, 1950 2,540,314 Amundsen Feb. 6, 1951 2,949,338 Linn et a1 Aug. 16, 1960 2,975,082 Henricks Mar. 14, 1961 FOREIGN PATENTS 469,875 Canada Dec. 5, 1950 

1. AN AQUEOUS PHOSPHATING SOLUTION HAVING A TOTAL ACIDITY WITHIN THE RANGE FROM ABOUT 5 TO ABOUT 100 POINTS AND CONTAINING AS ESSENTIAL INGREDIENTS THE PHOSPHATE ION AND THE ANION OF A POLYHYDROXY ALIPHATIC MONOCARBOXYLIC ACID HAVING AT LEAST 5 CARBON ATOMS AND AT LEAST 3 HYDROXY GROUPS. 